1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing regularly arranged package of coagulated grains by making use of flocculation and coagulation of polymer latex particles obtained by emulsion polymerization, etc.
2. Description of the Prior Art
When recovering from polymer latex resinous polymer being its dispersed phase, generally, an aqueous solution of coagulant such as inorganic salts, acids, etc., is put into the latex, or conversely, the latex is put into such an aqueous solution of coagulant, whereby the latex is coagulated in the liquid phase and turned into a state of slurry by such an operation as heat treatment, etc., thereafter, to be in the state of powders or grains through dehydration and drying. However, in this method, the configuration of powder is amorphous, powder or grain diameter is difficult to adjust and the grain diameter distribution is broad, thus, the substantial amount of fine powders being contained therein. As a result, loss by scattering, frequent occurrence of process trouble due to blending with fine powders, deterioration of work environment resulting from dust generation, increased danger of dust explosion and other untoward incidences have been brought about.
For the purpose of overcoming these problems, very ardent efforts have been made in synthetic resin manufacturing field; for example, there have been proposed a method for recovering polymer latex as spherical coagulated grains by spraying it into a coagulable atmosphere or a method of recovering spherical coagualated grains by having coagulated grains absorbed in organic solvent droplets dispersed into water phase and, then, through removal of the solvent and solidification of coagulated matters.
The former method is disadvantageous in that its industrial application is difficult for manufacturing grains larger than 500 .mu.m or for manufacturing highly heat resistant polymers having softening temperatures higher than 80.degree. C. and that it is difficult to closely pack the grain interior, while the latter method has raised problems in the aspects of cost, quality, applicable range, grain characteristics, etc., that in addition to the difficulty in removal of solvent and inclusions and in close packing of grain interior, no organic solvents which are compatible with utilization of said method are available, depending on type of polymers. As a background of development of such a variety of recovery methods, there lies the current of the times that the degree that the acceptability of characteristics such as the particle size or its distribution or size or packing rate, etc., rather than the physical properties of polymers, influences the quality of the product is increasing.
And as a method for obtaining solid by directly drying latex, spray drying or vacuum granulation drying is available and numerous contrivances have been applied. With these methods, however, removal of inclusions in the latex is difficult, scale-up of facilities is required, when forming larger grains, and in addition, large amount of thermal energy is necessary with low density latices, resulting in high treating costs; thus, they are largely subject to restriction in the aspect of quality and cost.
On the other hand, the present inventors previously filed a patent application (European Publication No. 0217006) for an invention for obtaining nearly spherical grains as one which will overcome the above-mentioned disadvantages at once, in which coagulated grains grown with coagulant units dispersed and scattered into an aqueous particle colloid, to have the colloidal particles coagulated on the outer surfaces of these units, thereby laminating them from inside out.
As a result of subsequent examinations based on the previous invention, they found out the fact that when coagulated grains are intended to have by continuous operation, mere continuous supply of polymer latex and coagulant into a stirring tank will result in formation of a large mass of coagulum and growth of coagulated matters on the tank wall surface, stirrer, etc., or settling and accumulation of formed coagulated grains at the tank bottom, causing blockaded discharge port and the like problems, and the fact that as a consequence, not only continuation of long continuous operation is thwarted, but sometimes yiels is extremely lowered, and operability being dreadfully impeded. Further, when coagulant is merely added to the polymer latex liquid surface, the coagulant or the coagulated matters tend to float due to surface tension, forming united grains or amorphous grains, thus inviting reduced yield and lowered product quality. Accordingly, for realization of industrial production by this coagulation process, there has arisen a need for developing a method and apparatus which enables long and continuous production of spherical coagulated grains with a uniform grain diameter, by providing solutions to the aforementioned problems.